As described in U.S. Patent Application Publication 2006/0157924, hereby incorporated by reference herein, in a web printing press, a web or webs may be printed in various printing units. The webs then may enter a folder superstructure. There, the webs may be slit into ribbons, which are then superimposed to form a ribbon bundle, before passing to a former. The ribbon bundle in the folder superstructure may be drawn over a roller at the top of the former called an RTF by driven nip rolls located after the nose of the former. The ribbon bundle then may pass to a folder where the ribbon bundle is cut into signatures.
The nip rolls may be spring-loaded against each other in an adjustable manner so as to set the pressure or “squeeze.” Nip rolls with urethane or rubber outer layers are known. These rubber or urethane coatings are incompressible, as no air, microspheres or other gas inclusions are added to make them compressible. U.S. 2006/0157924 describes a folder superstructure in which these nip rolls, which are located downstream of the former, have a compressible outer layer. This compressible outer layer can be made of microcellular foamed urethane or foamed rubber, and may have a Poisson's ratio of 0.5 or less. The microcellular foamed urethane may, for example, be 40 durometer with a poisson's ratio of 0.35.
A ribbon bundle may, for example, have six ribbons. The draw nip of the nip rolls can create uneven upstream longitudinal tensions of the different ribbons. A small change in nip pressure can also create large ribbon tension changes. To address uneven web tensions, gathering rolls or additional driven pull rolls upstream of the RTF are known.
Sometimes, the RTF can be a hard roll paired with a relatively soft nip roll. The nip that may be formed by the hard-soft nip roll often produces tension differences among the ribbons that pass through the nip. The RTF nip may be effective in both reducing the amount of air entrained between the ribbons as well as reducing the lateral motion of the ribbons along the RTF roll.